Selective weed discrimination

ABSTRACT

An apparatus ( 22 ) for selectively discriminating vegetation or plant matter ( 28 ) comprises a light emitting means ( 24 ), a light sensing means ( 30 ) and a distance sensing means ( 34 ). The light emitting means generates a beam of light ( 26 ) that can be directed onto plants or plant matter moving relative to the apparatus. The light sensing means senses light transmitted from said light emitting means and reflected from the plants or plant matter, and generates a reflection signal in response to the sensing of the reflected light. The distance sensing means senses the relative distance moved and generates a distance signal. A processing means ( 32 ) is operatively connected to the light sensing means and the distance sensing means to combine the reflection signal and distance signal to discriminate different types of plants or plant matter.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus fordiscriminating different types of ground vegetation in agriculture andrelates particularly, but not exclusively, to an agricultural boom spraythat incorporates such an apparatus.

BACKGROUND TO THE INVENTION

Over the last couple of decades broad acre spraying has become anessential component of crop management on most farms in Australia.Chemical companies have developed new chemical pesticides for killingweeds, insect pests and diseases which attack cash crops. The mostcommonly used technique for broad acre spraying of pesticides is the useof boom sprays, which may be self-propelled or towed behind anothervehicle. A typical boom spray has a plurality of spray nozzles mountedat spaced locations along a boom, a large tank for containing the sprayliquid and a pump system for pumping the liquid to the nozzles. Acontrol system is usually provided for controlling the rate at which thepesticide is sprayed relative to ground speed, and a marker system maybe used to aid driving and avoid overlapping.

One of the disadvantages of conventional boom sprays is that herbicidesare sprayed indiscriminately on the crop, bare ground and weeds. This isof concern in the case of food crops, with consumer groups becomingincreasingly vocal about chemical residue in crops and livestock. Thereis also an economic disincentive since a much greater volume of chemicalspray must be applied per hectare than is actually required toeffectively control the weeds.

Co-pending Australian patent application No. 16482/99 describes a methodand device for discriminating different types of ground vegetation inagriculture in which an artificial light source is employed fordirecting a beam of light onto the vegetation. A sensor assembly isprovided for detecting reflected radiation from the vegetation in aselected wavelength band and generating a sensing signal in response tothe detection. A logic controller determines whether a magnitude of thesensing signal falls within a predetermined range of values in order todistinguish one type of vegetation from another type. In the red andnear infrared wavelengths there is some variation in reflectance fromone plant to another, depending on a number of factors. The logiccontroller compares the amplitude of the sensing signal with a decisionwindow. If the amplitude of the incoming sensing signal falls within thedecision window then the logic controller determines that a certain typeof plant has been detected and activates the corresponding solenoidvalve to deliver a dose of spray liquid from a spray nozzle to thetargeted weed.

With certain types of vegetation, it is not possible to distinguish weedfrom crop plants based on the sensing of the reflected radiation alone.Therefore, AU 16482/99 also describes the use of a plurality of sensorsarranged in an array with a geometric configuration adapted to aid indiscriminating different types of vegetation. For example, a lineararray of three sensors can be adapted to distinguish a stem type targetvegetation such as, for example, skeleton weed (Chondrilla juncea L.). Aunique decision window for each sensor in the array is programmed intothe logic controller in order to detect sensing signals which fallwithin respective decision windows. By a judicious choice of geometricarray of sensors and providing a unique decision window for each sensor,the logic controller can accurately distinguish between different shapedplants.

Whilst the above arrangement of sensors in a geometric array works verywell, in practice the need to change the geometric array for each typeof weed desired to be distinguished is rather inconvenient.

SUMMARY OF THE PRESENT INVENTION

The present invention was developed with a view to providing a moreefficient method and apparatus for discriminating different types ofground vegetation in agriculture, without the need to change hardwarecomponents of the apparatus every time a different type of plant is tobe discriminated. Although the invention will be described primarilywith reference to the selective spot spraying of weeds, it will beapparent that the method and apparatus for discriminating differenttypes of ground vegetation may also be used to identify weeds formechanical destruction, mapping of weed infestation coupled with aglobal positioning system (GPS) or differential global positioningsystem (dGPS), differentiated spraying of liquid fertiliser on cropplants, measurement and logging of crop vigour, and other weed and cropmanagement practices. It will also be apparent that the invention is notlimited in its application to broadacre farming but may also, forexample, be applied to intensive row crop farming, or identification forsorting of plant matter such as fruit or other produce

Throughout this specification the term “comprising” is used inclusively,in the sense that there may be other features and/or steps included inthe invention not expressly defined or comprehended in the features orsteps subsequently defined or described. What such other features and/orsteps may include will be apparent from the specification read as awhole.

Throughout this specification the term “light” is to be understood toinclude electromagnetic radiation in the visible as well as theinvisible spectrum, and thus includes, for example, radiation in theinfra-red as well as the near infra-red regions.

According to one aspect of the present invention there is provided anapparatus for selectively discriminating vegetation or plant matter, theapparatus comprising:

light emitting means for generating a beam of light that can be directedonto plants or plant matter over which the light emitting means movesrelative to the plants or plant matter;

light sensing means for sensing light transmitted from said lightemitting means and reflected from said plants or plant matter, andgenerating a reflection signal in response to said sensing;

distance sensing means for sensing the relative distance moved inrelation to said plants or plant matter by said light emitting means andgenerating a distance signal in response to said sensing; and,

processing means operatively connected to said light sensing means anddistance sensing means for combining said reflection signal and distancesignal whereby, in use, different types of plants or plant matter,including weeds, can be discriminated.

Preferably the processing means combines the reflection signal anddistance signal to determine the size and/or shape of the plant or plantmatter.

Preferably said distance sensing means includes a wheel encoder forsensing the speed at which a vehicle on which the apparatus is mountedis moving over the ground. Typically said wheel encoder generates asignal in the form of a train of pulses or pulse count, wherein thefrequency of the pulses is directly proportional to the speed at whichthe vehicle moves over the ground, as well as the distance it hastravelled. Preferably a separate wheel encoder is provided on each sideof the vehicle, so that the processing means is able to identify thedistance the vehicle has travelled, when the vehicle is turning, as wellas the speed at which it is turning, and adjust the responseaccordingly.

In one embodiment said light emitting means comprises a plurality ofartificial light sources, each light source being adapted to transmit abeam of light at different wavelengths, whereby, in use, the reflectionsignal at each wavelength is used by the processing means in combinationwith the distance signal to discriminate plants or plant matter.

Preferably the processing means is programmed to combine the reflectionsignal and distance signal to discriminate one type of plant matter fromanother type of plant matter and/or one type of plant matter from nonplant matter.

Preferably said light sensing means comprises a plurality of sensorassemblies mounted in an array. Preferably each sensor assemblycomprises a pair of sensors mounted in close proximity and each adaptedto detect the reflected light at different wavelengths. Typically thesensors employed are photodiodes. Preferably a first sensor in eachassembly is adapted to generate a sensing signal when it detectsreflected light having a wavelength peaking between 550 nm and 650 nm.Preferably a second sensor in each assembly is adapted to generate asensing signal when it detects reflected light having a wavelengthpeaking between 850 nm and 950 nm.

Preferably each sensor assembly includes one or more further sensorsadapted to generate a sensing signal when each further sensor detectsreflected light having a predetermined wavelength in the visible, nearinfra-red or infra-red wavelength bands, wherein the processing means isoperatively connected to the further sensors, wherein the sensingsignals from the further sensors are used to discriminate plants orplant matter.

Preferably the first and second sensors are mounted concentrically inorder to reduce the incidence of “false positive” spectral responses, inthat if the second sensor reads reflected light from a target, that sametarget must also have passed under the first sensor.

Preferably the further sensors are mounted concentrically with the firstand second sensors.

Preferably the processing means is configured to produce an outputsignal when a target plant is identified or when an object that is notthe target plant is identified. Preferably the apparatus includes aresponse means arranged to provide a response to the output signal.Preferably the response means is one or more of: a solenoid valvearranged to operate a means for spraying the target plant or object; avalve means arranged to operate a means for distributing a powder orparticulate material; a recording means for recording the presence (orabsence) and location of the target plant or object; a cutting means forcutting material in response to identification of the target plant orobject; or a cultivating means, such as an actuator for a hoe.

According to another aspect of the present invention there is provided amethod for selectively discriminating vegetation or plant matter, themethod comprising the steps of:

generating a beam of light that can be directed onto plants or plantmatter over which the light emitting means moves relative to the plantor plant matter;

sensing light transmitted from said light emitting means and reflectedfrom said plants or plant matter, and generating a reflection signal inresponse to said sensing;

sensing the distance moved relative to said plants or plant matter bysaid light emitting means and generating a distance signal in responseto said sensing; and,

processing said reflection signal and distance signal to determine thespectral characteristics and size and/or shape of the plants or plantmatter whereby, in use, different types of plants or plant matter,including weeds, can be discriminated.

Preferably the light is sensed by one or more sensor assemblies havingone or more sensors. Preferably as the sensor assemblies travel over theground each of the sensors in the sensor assemblies continually senseslight reflected upwards from the ground surface. Alternatively theplants or plant matter travel underneath stationary sensor assemblies,wherein each of the sensors in the sensor assemblies continually senseslight reflected from the plants or plant matter.

However, preferably when a first affirmative spectral response occurs,the processing means begins to “strobe” the sensor assemblies so thatthey only operate to sense the presence or absence of the target plantmatter at discretely spaced intervals.

Preferably readings from each of a plurality of sensor assemblies usedfor sensing the reflected light are taken at uniformly spaced intervalsover the ground surface, and are typically triggered by pulses generatedvia a wheel encoder used for sensing the distance travelled over theplants. Typically the interval spacing is set at a fixed distance,typically between 0.2 mm and 2 mm when travelling in a straight line.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In order to facilitate a more detailed understanding of the nature ofthe invention a preferred embodiment of an apparatus and method fordiscriminating different types of ground vegetation will now bedescribed in detail, by way of example only, with reference to theaccompanying drawings, in which:

FIGS. 1( a) and (b) illustrate a boom spray which incorporates anapparatus for discriminating different types of ground vegetation inaccordance with the present invention;

FIGS. 2A and 2B are schematic illustrations of a preferred embodiment ofthe apparatus for discriminating different types of ground vegetationemployed in the boom spray of FIG. 1;

FIG. 3 illustrates schematically the method for discriminating differenttypes of ground vegetation in accordance with a preferred embodiment ofthe invention;

FIG. 4 illustrates a preferred embodiment of a pair of sensors employedin the apparatus of the present invention;

FIG. 5 illustrates graphically the spectral reflectance of various typesof plants;

FIG. 6 illustrates the operation of a selective spraying apparatusincorporating a preferred embodiment of the apparatus for discriminatingdifferent types of ground vegetation;

FIG. 7 illustrates the use of dGPS to record the location of a selectedtype of vegetation; and,

FIG. 8 illustrates in more detail a processing means of the apparatus inFIG. 2C.

FIGS. 1( a) and (b) illustrate a typical agricultural spraying apparatusknown as a boom spray, in this case of the kind that is towed behindanother vehicle, tractor 10. The boom spray is in the form of a traileron which is mounted a large tank 12 for containing the spray liquid,typically a herbicide or other chemical pesticide. A pump system(comprising pump, tank, pipework and valves etc, not shown) pumps thespray liquid to a plurality of nozzles 14 mounted at spaced locationsalong a transversely mounted boom 16. A spray liquid supply line 18which extends the full length of the boom supplies the herbicide to eachof the spray nozzles 14. An apparatus 22 for discriminating differenttypes of ground vegetation is mounted on the boom spray and controls thedelivery of spray liquid from the nozzles 14 depending on the type ofvegetation distinguished by the apparatus 22.

One embodiment of the apparatus 22 for discriminating different types ofground vegetation is illustrated schematically in FIG. 2A. The device 22comprises an artificial light emitting means 24 for directing a beam 26of light onto the vegetation 28. In this embodiment, the light emittingmeans 24 is a pair of light emitting diodes (LEDs) and associatedlensing that emit light at a wavelength of 635 nm and 875 nmrespectively. However any suitable artificial light emitting means maybe employed such as a wide-spectrum quartz halogen lamp or a laser. Theuse of LEDs is particularly advantageous as it enables light beams to begenerated at the particular wavelengths of interest with low powerconsumption. In this connection, one or more LEDs adapted to emit lightat selected wavelengths may be employed for light emitting means 24. Asensor assembly 30 for detecting light from the LEDs 24 reflected fromthe vegetation 28 in a selected frequency band is also provided, andtypically includes a lens system for focusing on the vegetation. One ormore filters may be employed to permit light in selected frequency bandsto pass through to the sensor assembly 30. Sensors in the sensorassembly 30 generate a sensing signal in response to detection of thereflected light.

The apparatus 22 also includes a processing means, in this case in theform of a microprocessor-based controller 32 for determining whether amagnitude of the sensing signal from the sensor assembly 30 falls withina predetermined range of values. The predetermined range of values ordecision window is programmed into the controller 32 so that it is ableto distinguish one type of vegetation from another type based on themagnitude of the sensing signal from the sensor assembly 30.

The apparatus 22 further comprises a distance sensing means, which inthis embodiment includes a wheel encoder 34 for sensing the speed atwhich the trailer on which the apparatus 22 is mounted is moving overthe ground. Wheel encoder 34 is operatively connected to the controller32 and generates a signal in the form of a train of pulses or pulsecount. The frequency of the pulses is directly proportional to the speedat which the trailer moves over the ground, and provides informationregarding the distance it has travelled. Controller 32 is able tocalculate the actual distance travelled based on the diameter of thetrailer wheels 36. Wheel encoder 34 detects the speed at which a wheel36 of the trailer on which the apparatus 22 is mounted moves. Anysuitable type of wheel encoder may be employed.

For example, one form of wheel encoder comprises a shaft geared to thewheel axle and is adapted to generate 2000 encoder pulses perrevolution. In the described embodiment, a flywheel gear is provided onthe wheel axle adjacent one of the wheels 36 on both sides of thetrailer. A sensor is mounted adjacent the rim of the flywheel and isadapted to generate a pulse every time it detects one of the teeth onthe flywheel rim. The train of digital pulses or pulse count thusgenerated is received by the controller 32 to calculate the distancetravelled by the trailer, and hence by the sensor assembly 30 as ittravels over the ground. Preferably a separate wheel encoder is providedon each side of the trailer, so that the controller 32 is able toidentify when the trailer is turning, as well as the speed at which itis turning, and adjust the response time along the length of the boomaccordingly. This data is processed by controller 32 to providecompensation for turning and this compensation ensures that like plantspecies are similarly identified irrespective of curvature of travel.Although the use of two wheel encoders is the preferred arrangement, thesystem will still function with one wheel encoder only.

FIG. 2B shows the apparatus 22 including the controller 32 in moredetail. Controller 32 includes an amplifier means 74, an “AND gate”means 76, trimpots 78 and a microprocessor 80. Signals from sensorassembly 30 are provided to the amplifier means 74 by connection 88. Thesignals are boosted by the amplifier means 74 and then provided to theAND gate means 76. The trimpots 78 provide adjustable minimum andmaximum reference levels to the AND gate means 76. The reference levelsare used to trigger the AND gate means 76 when the input signal from theamplifier means 74 falls within the minimum and maximum referencelevels. The reference levels are set according to the desired level ofreflectance received by the sensor assembly 30 to indicate the presenceof selected vegetation as will be described in more detail below. Therange of values between the minimum and maximum reference levels set ineach trimpot are referred to as the “decision window” in the descriptionbelow. Triggering of the AND gate means 76 indicates to themicroprocessor 80 that the required level of reflectance has beendetected by the sensor array 30. Input signals from the wheel encoder 34are transmitted by connection 100 to the microprocessor 80. Outputs 104and 106 from the microprocessor will be described in more detail below,as will input/output 108.

By combining the reflection signal information received from the sensorassembly 30 with the distance information provided by the wheel encoder34, controller 32 is able to determine the plant matter characteristics,such as leaf characteristics. Plant matter characteristics include thespectral response and size and/or shape of the leaves, fruit or plantparts of the ground vegetation. Determining the plant mattercharacteristics enables discrimination between different types of plantsas the apparatus travels over the ground. The method by which it doesthis will be described in more detail below with reference to FIGS. 3, 4and 5.

A pump and chemical supply system 38 is provided with a plurality ofhigh speed solenoid controlled valves 40 for controlling the delivery ofspray liquid from each nozzle 14. The solenoid controlled valves 40 arealso under the control of microprocessor-based controller 32, viaconnection 104. Hence, when the controller 32 detects the presence of,for example, a weed on the basis of the combination of the sensingsignal information generated by the sensor assembly 30 and the distancepulses generated by the wheel encoder 34, it activates the solenoidcontrolled valve 40 to release a jet of spray liquid from the nozzle 14onto the weed.

Preferably a shroud 20 is suspended from the boom 16 as shown in FIG. 1,in order to minimise the amount of sunlight which might reach thesensors and interfere with the detection of reflected radiation. Shroud20 is made from a flexible, light-impervious material and is ofsufficient length to shade any vegetation directly below the LEDs 24 andsensor assembly 30 from direct sunlight throughout most of the day. Ifthe apparatus is operated after dark, the shroud 20 may be dispensedwith.

Preferably the boom 16 is designed to travel at a fairly constant heightas it moves over the ground, so as to minimise variations in theintensity of the reflected light due to changes in the distance of thelight source 24 and the sensor assembly 30 from the ground vegetation.Preferably, the sensor assembly is maintained at a height of between 10mm to 1000 mm above the target vegetation, more preferably between 200mm to 800 mm above the target vegetation. Although it has been foundthat the magnitude of the sensing signal does vary with changes inheight, these variations are smaller than the difference in magnitudeproduced by the absorption of electromagnetic radiation by differenttypes of vegetation in selected frequency bands.

Only one light source 24 and sensor assembly 30 are shown in FIG. 2A.However, typically a plurality of sets of light sources and sensorassemblies are provided on the boom spray, located at a distance forward(relative to the direction of travel of the boom) of the spray nozzles14. One or more sets of light sources and sensor assemblies are used tocontrol a respective spray nozzle 14 in order to discriminate the typeof vegetation in the target area of each spray nozzle 14.

Preferably, each sensor assembly 30 comprises a pair of sensors mountedin close proximity and each adapted to detect the reflected light atdifferent wavelengths. Preferably, the sensors employed are photodiodes.A first sensor 44 is adapted to generate a sensing signal when itdetects reflected light having a wavelength peaking between 550 nm and650 nm. Preferably, the second sensor 46 is adapted to generate asensing signal when it detects reflected light having a wavelengthpeaking between 850 nm and 950 nm.

A series of experimental measurements were made to determine thespectral reflectance of various plants. The results in the form of thenormalised reflectance measurements plotted against wavelengthmeasurements in nanometres are illustrated in FIG. 5. It was found thatwith virtually all green leafed plants, the reflectance rises sharply atapproximately 700 nm, whereas below this wavelength, very little lightis reflected from the plant matter (represented by lines 62 and 64 inFIG. 5). On the other hand, dry, brown plant matter, such as stubble (inside view) continues to have a relatively strong reflectance below 700nm, as represented by the line marked 60. Above 700 nm, the stubble hasa similar reflectance characteristic to that of the green leaf plants.Stubble in end view has a characteristic indicated by 66.

Therefore, by using two sensors, a first sensor 44 for detecting thereflected light at approximately 630 nm and a second sensor 46 fordetecting the reflected light at approximately 920 nm (represented bythe dotted lines in FIG. 5), it is possible to distinguish between thebrown stubble and green leaf plant matter. Namely, if a high sensingsignal is generated by both sensors 44 and 46, it indicates that thevegetation is probably stubble, whereas if a high sensing signal isbeing generated by the second sensor 46, and a low or zero sensingsignal is being generated by first sensor 44, it indicates that a greenleaf plant has been detected, hereafter referred to as an affirmativespectral response. Controller 32 applies the appropriate logic in orderto discriminate between different types of plant matter.

FIG. 5 also illustrates how the magnitude of the sensing signalgenerated by the second sensor 46 may be used to discriminate betweendifferent types of green vegetation. By selecting the appropriate upperand lower limits of each decision window, the controller 32 can incertain circumstances distinguish between different types of greenvegetation. At 920 nm, the reflectance characteristic 62 for typicalgreen leaf plant No. 1 has a normalised reflection value falling between1.6 and 1.8, whereas the reflectance characteristic 64 of the typicalgreen leaf plant No. 2 has a normalised reflectance value fallingbetween 1.2 and 1.4. However, with some vegetation it is not possible todistinguish between the different plants based on the sensing signalgenerated by the reflected light alone, as the spectral reflectancecharacteristic is practically indistinguishable. For this reason, theapparatus 22 is also capable of distinguishing the size and/or shape ofthe plant material. The preferred method of detecting the shape and/orsize of the plant material will now be described with reference to FIG.3.

A plurality of sensor assemblies 30 are shown arranged in a linear arrayin FIG. 3. As the apparatus travels over the ground in the direction oftravel as indicated by arrow A it passes over a plant leaf 50 near theground. Each of the rectangular strips shown in broken outline in FIG. 3represents a discrete position of the sensor array as it travels abovethe ground surface. Preferably, as the sensor array travels over theground each pair of sensors 44, 46 in the sensor assemblies 30continually senses light reflected upwards from the ground surface, overthe ground section M. Location 52 represents the position at which oneof the sensor assemblies first detects the presence of target vegetationand generates an affirmative spectral response. When this firstaffirmative spectral response occurs, controller 32 changes theillumination to “strobe” the light emitting means 24 and/or discretelysamples the sensor assemblies 30 so that it only operates to sense thepresence or absence of the target plant matter at discretely spacedintervals, in this case at positions 1 to 12 of the sensor array 48, ie,over ground section N.

At pulse position 12, none of the sensors generate an affirmativespectral response, and thus the pulsing ceases, and the system revertsto a continuous sensing mode, over ground section P. In this embodimentthe most efficient operation of the electronics is achieved by thestrobing being in operation only when an affirmative spectral responseis recorded (ie, ground section N), and reverts to continuous mode atother times. However the system can be fully effective even if thestrobing were to operate at all times.

Preferably, readings from each of the sensor assemblies 30 are taken atuniformly spaced intervals over the ground surface, and may betriggered, for example, by the pulses generated via the wheel encoder34. The interval spacing is set at a fixed setting, typically between0.2 mm and 2 mm when travelling in a straight line, and when travellingon a curve varies according to the turning circle. Controller 32 is thenable to combine the information obtained from the sensing signalgenerated by the sensors 44 and 46, together with the distance travelledbetween each reading of the sensors to determine the width of the plantleaf 50 in the direction of travel. If desired, controller 32 can alsocombine the signals received from adjacent sensor assemblies 30 in orderto determine the approximate size and shape of the plant leaf 50.

Preferably the first and second sensors 44 and 46 are provided in closeproximity, typically immediately adjacent each other as shown in FIG. 3.In order to obtain an affirmative spectral response the signal outputfrom the first sensor 44 (550 nm to 650 nm) must be reading low and thesignal output from the second sensor 46 (850 nm to 950 nm) must bereading high at the same time. However, if the first and second sensors44 and 46 are positioned side by side as shown in FIG. 3, it is possiblefor example for the apparatus when passing over a piece of stubble lyingat an oblique angle to the direction of travel A to record a highreading on the second sensor, and positioned so that it is not under thefirst sensor, but by the time it passes under the first sensor it hasgone past the second sensor. There is a possibility in this sensorconfiguration for a thin plant such as stubble being read by the twosensors sequentially rather than simultaneously. Hence, there is a briefmoment when the first sensor would read low, and the second sensor wouldbe reading high. This is the condition for an affirmative spectralresponse, however the reading obtained is in fact a “false positive”.However, if the first and second sensors 44 and 46 are mountedconcentrically as shown in FIG. 4, it is possible to reduce theincidence of “false positives” because both sensors must read the targetsimultaneously. For a green leaf to achieve an affirmative spectralresponse with the concentric sensors it first needs to cross the firstsensor 44 before it reads high on the inner second sensor 46. If a pieceof stubble were to cross the concentric sensor arrangement, it wouldread high on both sensors 44 and 46, which would not constitute anaffirmative spectral response.

A suitable arrangement of lenses and/or filters 72 may be employed inconnection with either one or both of the light sources 24 and thesensor assembly 30 in order to better focus the light beam 26 and/or thereflected light onto the sensors in the sensor assembly. Thus, eachsensor will preferably have a narrow field of view. Several differentarrangements are described in AU16482/99 and will not be described againhere.

FIG. 6 illustrates the preferred method of operation of the apparatusfor distinguishing different types of ground vegetation in itsapplication to precision spot spraying of weeds. FIG. 6 illustrates thesequence of operation in four steps moving down the page as theapparatus moves over the plant 28 in the direction of travel of the boomspray. In FIG. 6A, the sensor-head approaches the plant 28 and as thesensor assemblies 30 continuously scan the ground the controller 32records the ground reading and under “non-strike” conditions the spraynozzle 14 remains closed. In FIG. 6B, the sensor assemblies 30 aredirectly over the plant 28. Controller 32 processes and interprets theinformation received from the sensor assemblies 30 and the wheel encoder34 for colour, shape and size of the plant leaf. If controller 32recognises the characteristics for a target, such as a weed, thecontrollers 32 registers that the target is detected, hereafter referredto as a “strike”. It is noted that the controller 32 may be programmedto register “strikes” for a plurality of targets. At FIG. 6C, if astrike has been registered, the controller sends a signal to thesolenoid control valve for the spray nozzle 14. At FIG. 6D, the controlof the opening and closing of spray nozzle 14 is determined bycontroller 32 using information received from the wheel encoder 34, sothat only that particular plant 28 is sprayed.

The controller 32 may be connected by connection 108 to a differentialglobal positioning system (dGPS) 70. Referring to FIG. 7, as theapparatus 22 passes over a selected plant the position of the plant canbe recorded by the dGPS 70. A signal received from global positioningsystem satellites 92 can provide location information to the apparatus22 so that the position of the plant can then be recorded for laterspraying or for monitoring purposes.

Referring to FIG. 8, controller 32 is described in more detail. Thecontroller includes a printed circuit board on which are mountedamplifier means 74 AND gate means circuitry 76, trimpots 78 andmicroprocessor 80. When an optical sensor 30 receives light reflectedfrom vegetation the output voltage from each of the sensors 30 isreceived by connection 88. First signal 100 is received from the firstsensor 44, second signal 98 is received from the second sensor 46.Signal 1 and signal 2 are amplified by amplifiers 96 and 94respectively. Outputs of the amplifiers 96 and 94 are received by theAND gate 76.

A predetermined range of values for a decision window is programmed intothe microprocessor 80. From these values, the microprocessor setsdigital trimpots 82 and 84 to the upper and lower values of the decisionwindow for each respectively.

If the value of the amplified signal 100 falls within the decisionwindow set in trimpot one 84, and if the value of the amplified signal98 falls within the decision window set in trimpot two 82, the spectralreflectance criteria have been met to constitute an affirmative spectralresponse. The input signal 102 from the wheel encoder provides themicroprocessor 80 with information to determine leaf size and thereforediscriminate vegetation being sensed. A “strike” will be registered onlyif both the spectral criteria and leaf criteria have been met.

Software for controlling the microprocessor 80 may be downloaded by anexternal connection 86. Once the microprocessor is programmed thesoftware is stored in storage means, such as FlashRAM or EEPROM withinor connected to the microprocessor. Other suitable storage means canalso be employed such as a hard disk drive.

Depending on the programming the output signal is then sent to an outputdevice by connection 104, which may be for example a storage system forstoring the location from the dGPS 70 and/or a control signal to openthe solenoid valves 40. In the case of the microprocessor beingprogrammed to open or close the spray valves 40, it may be programmed toopen a selected distance before the target plant and close off aselected distance after the target plant. This can be desirable toensure the weed is sprayed when travelling at high speeds to ensurethere is sufficient overspray as required by some chemical treatments ofweeds. In the case of liquid fertilisers it may be desirable to spraythe ground in the proximity of the plant as well as the plant itself.Additionally it is possible to select the output operation within thesoftware to spray fertiliser on cash crop plants, but not on weeds.

In summary the logic contained within the programming can effect manypractical applications in agriculture including:

-   1. Select a Single Species Only

This is applied in a situation where it is the objective to reduce theincidence rate of a problem weed species, or to utilise specificherbicides on problem weed species, or to apply a liquid to one species,or to log the location of those plants

-   2. Select the Cash Crop Only

This can be used to apply fertilisers or pesticides to crops only.

-   3. Select a Group of Weed Species

This would be applied in a situation where it is the objective to reducethe incidence rate of a number of problem weed species, such as wherethe objective is to treat multiple weed species, or where a group ofspecific weeds develop tolerance to broad-spectrum herbicides.

-   4. Select all Weeds With the Exception of the Crop

This is applied for selectively spraying of weeds-only withoutsubstantially over-spraying either the crop or the ground, or formechanical destruction of weeds-only. This is useful for precision weedmanagement in most types of agricultural crops including pasture.

-   5. Measure Crop Vigour

In this application, the size and/or spectral response of plant leavescan be logged as an indicator of plant vigour across a paddock.Discolouration or stunted or malformed growth may indicate disease orother growth impediments, which can be identified.

-   6. Produce Row Cropping Data

The size of plant growth within crop rows can be measured and logged.

7. Discrimination of Fruit/Vegetables

It is possible to discriminate plant matter aside from individualleaves, such as fruit/vegetables, by their size/shape and spectralresponse. The size, shape and/or colour (spectral response) of fruitand/or vegetables can be measured and logged. This can be useful todetermine, say, whether a crop is ripe and ready for harvesting or foridentification in sorting after picking. In this example the sensorassembly may be stationary and the plant matter may be moving on aconveyor. The distance sensing means would sense the distance moved bythe conveyor.

-   8. Discrimination of Foreign Objects

It is possible to discriminate non plant matter from plant matter of aplant by the size/shape of the target and the spectral response. Foreignobjects could include insects of sufficient size. Other foreign objectsmay include rubbish or debris blown onto a crop. Foreign objectsidentified as, say, an insect could be sprayed with an insecticide.

-   9. Other Applications

Because of the flexibility of the system there are other uses for thetechnology, namely in the remote sensing of noxious weeds (e.g. skeletonweed) or as a research tool for determining the distribution of weeds tocrop ratio or to measure the overall stress levels of plants in general.

Now that a preferred embodiment of the apparatus and method fordistinguishing different types of ground vegetation have been describedin detail, it will be apparent that the apparatus and method providesignificant advantages over the prior art, including the following:

-   -   (a) distinguishing of different types of ground vegetation can        be effected more accurately;    -   (b) different types of ground vegetation can be detected by        software controlled modifications of the sensing logic employed        in the controller, rather than changes to the hardware of the        sensing array;    -   (c) relatively simple signal processing is required, thus        facilitating high speed searching for specific plants.

Numerous variations and modifications will suggest themselves to personsskilled in the relevant arts, in addition to those already described,without departing from the basic inventive concepts. For example, thenumber of different wavelengths of sensors may be more than the twodescribed in the preferred embodiments; more than two rings may be usedin the concentric ring configuration of the sensors; the sensor arraymay also employ a geometric configuration of sensors, and is not limitedto the simple linear array of the described embodiment. All suchvariations and modifications are to be considered within the scope ofthe present invention, the nature of which is to be determined from theforgoing description.

1. An apparatus for selectively discriminating vegetation or plantmatter, the apparatus comprising: light emitter for generating a beam oflight that can be directed onto plants or plant matter over which thelight emitter moves relative to the plants or plant matter; light sensorfor sensing light transmitted from said light emitter and reflected fromsaid plants or plant matter, and generating a reflection signal inresponse to said sensing; distance sensor arranged to measure therelative distance moved by said light emitter in relation to said plantsor plant matter and further arranged to generate a distance signal inresponse to said measurement; and, processor operatively connected tosaid light sensor and distance sensor for combining said reflectionsignal and distance signal whereby, in use, different types of plants orplant matter can be discriminated.
 2. An apparatus according to claim 1,wherein the processor combines the reflection signal and distance signalto determine the size and/or shape of the plant or plant matter.
 3. Anapparatus according to claim 1, wherein said distance sensor includes awheel encoder for sensing the speed at which a vehicle on which theapparatus is mounted is moving over the ground.
 4. An apparatusaccording to claim 3, wherein said wheel encoder generates a signal inthe form of a train of pulses or pulse count, wherein the frequency ofthe pulses is directly proportional to the speed at which the vehiclemoves over the ground, as well as of the distance it has travelled. 5.An apparatus according to claim 3, wherein a separate wheel encoder isprovided on each side of the vehicle, so that the processor is able toidentify when the vehicle is turning and adjust the responseaccordingly.
 6. An apparatus according to claim 1, wherein said lightemitter comprises a plurality of artificial light sources, each lightsource being adapted to transmit a beam of light at differentwavelengths, whereby, in use, the reflection signal at each wavelengthis used by the processor in combination with the distance signal todiscriminate plants or plant matter.
 7. An apparatus according to claim1, wherein the processor is programmed to combine the reflection signaland distance signal to discriminate one type of plant matter fromanother type of plant matter and/or one type of plant matter from nonplant matter.
 8. An apparatus according to claim 1, said light sensorcomprising a plurality of sensor assemblies mounted in an array.
 9. Anapparatus according to claim 8, each sensor assembly comprising two ormore sensors mounted in close proximity and each adapted to detect thereflected light at different wavelengths.
 10. An apparatus according toclaim 9, wherein the sensors employed are photodiodes.
 11. An apparatusaccording to claim 9, wherein a first sensor in each assembly is adaptedto generate a sensing signal when it detects reflected light having awavelength peaking between 550 nm and 650 nm.
 12. An apparatus accordingto claim 11, wherein a second sensor in each assembly is adapted togenerate a sensing signal when it detects reflected light having awavelength peaking between 850 nm and 950 nm.
 13. An apparatus accordingto claim 9, wherein each sensor assembly includes one or more furthersensors adapted to generate a sensing signal when each further sensordetects reflected light having a predetermined wavelength in thevisible, near infra-red or infra red wave bands, wherein the processoris operatively connected to the further sensors and the sensing signalsfrom the further sensors are used to discriminate plants or plantmatter.
 14. An apparatus according to claim 9, wherein two or moresensors are mounted concentrically in order to reduce the incidence of“false positive” spectral response.
 15. An apparatus according to claim1, wherein the processor is configured to produce an output signal whena target plant is identified or when an object that is not a targetplant is identified.
 16. An apparatus according to claim 15, wherein theapparatus includes a response means arranged to provide a response tothe output signal.
 17. An apparatus according to claim 16, wherein theresponse means is one or more of: a solenoid valve arranged to operate ameans for spraying; or a valve arranged to operate a means fordistributing a powder or particulate material; or a recorder forrecording the presence and location of the target plant and/or object; acutter for cutting material in response to identification of the targetplant or object; or a cultivator.
 18. A method for selectivelydiscriminating vegetation, or plant matter, the method comprising thesteps of: generating a beam of light that can be directed onto plants orplant matter over which a light emitter moves relative to the plant orplant matter; sensing light transmitted from said light emitter andreflected from said plants or plant matter, and generating a reflectionsignal in response to said sensing; sensing the distance moved relativeto said plants or plant matter by said light emitter and generating adistance signal in response to said sensing; and, processing saidreflection signal and distance signal to determine the spectralcharacteristics and size and/or shape of the plants or plant matterwhereby, in use, different types of plants or plant matter, includingweeds, can be discriminated.
 19. A method according to claim 18, whereinthe light is sensed by one or more sensor assemblies having one or moresensors.
 20. A method according to claim 19, wherein the sensorassemblies travel over the ground and each of the sensors in the sensorassemblies continually senses light reflected upwards from the groundsurface.
 21. A method according to claim 19, wherein the plants or plantmatter travel underneath the sensor assemblies and each of the sensorsin the sensor assemblies continually sensed the light reflected upwardsfrom the plants or plant matter travelling beneath.
 22. A methodaccording to claim 20, wherein when a first affirmative spectralresponse signal occurs, the processor begins to “strobe” the sensorassemblies so that they only operate to sense the presence or absence ofplant matter at discretely spaced intervals.
 23. A method according toclaim 22, wherein readings from each of a plurality of sensor assembliesused for sensing the reflected light are taken at uniformly spacedintervals over the ground surface, and are typically triggered by pulsesgenerated via a wheel encoder used for sensing the distance travelledover the plants.
 24. A method according to claim 23, wherein theinterval spacing is set at a fixed distance, typically between 0.2 mmand 2 mm when travelling in a straight line.